Light-Emitting Diode (LED) Devices Comprising Nanocrystals

ABSTRACT

The present invention provides light-emitting diode (LED) devices comprises compositions and containers of hermetically sealed luminescent nanocrystals. The present invention also provides displays comprising the LED devices. Suitably, the LED devices are white light LED devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/609,736, filed Oct. 30, 2009, which is a continuation-in-part of U.S.application Ser. No. 12/076,530, filed Mar. 19, 2008. U.S. applicationSer. No. 12/076,530 claims the benefit of U.S. Provisional PatentApplication No. 60/895,656, filed Mar. 19, 2007, and U.S. ProvisionalPatent Application No. 60/985,014, filed Nov. 2, 2007. The disclosuresof each of these applications are incorporated herein by reference intheir entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods light-emitting diode (LED)devices comprising luminescent nanocrystals, suitably white light LEDs.The present invention also relates to display systems comprising the LEDdevices.

2. Background of the Invention

Luminescent nanocrystals when exposed to air and moisture undergooxidative damage, often resulting in a loss of luminescence. The use ofluminescent nanocrystals in applications such as down-conversion andfiltering layers often expose luminescent nanocrystals to elevatedtemperatures, high intensity light, environmental gasses and moisture.These factors, along with requirements for long luminescent lifetime inthese applications, often limits the use of luminescent nanocrystals orrequires frequent replacement. There exists a need therefore for methodsand compositions to hermetically seal luminescent nanocrystals, therebyallowing for increased usage lifetime and luminescent intensity.

There also exists a need for light-emitting diode (LED) devicesutilizing hermetically sealed nanocrystals, including white light LEDdevices.

BRIEF SUMMARY OF THE INVENTION

In one embodiment, the present invention provides light-emitting diode(LED) devices. The LED devices suitably comprise a blue-light emittingLED and a hermetically sealed container comprising a plurality ofluminescent nanocrystals. The container is placed with respect to theLED to facilitate down-conversion of the luminescent nanocrystals.

Suitable hermetically sealed containers include plastic or glass tubes,such as glass capillaries. In exemplary embodiments, hermetically sealedcontainer is spaced apart from the LED. Suitably, the luminescentnanocrystals emit green light and red light. Exemplary the luminescentnanocrystals for use in the LED devices comprise CdSe or ZnS, includingluminescent nanocrystals that are core/shell luminescent nanocrystalscomprising CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS.In exemplary embodiments, the luminescent nanocrystals are dispersed ina polymeric matrix. The present invention also provides display systemscomprising the LED devices.

In further embodiments, the present invention provides light-emittingdiode (LED) devices comprising an LED, a hermetically sealed containercomprising a plurality of luminescent nanocrystals optically coupled tothe LED and a light guide optically coupled to the hermetically sealedcontainer. Suitably, a first portion of light emitted from the LED isdown-converted by the luminescent nanocrystals, and a second portion oflight emitted from the LED, and the down-converted light from theluminescent nanocrystals, are emitted from the light guide.

In exemplary embodiments, the LED emits blue light. Suitably, the firstportion of blue light emitted from the LED is down-converted by theluminescent nanocrystals to green light and red light. The secondportion of blue light, the green light and the red light suitablycombine to produce white light.

Exemplary hermetically sealed containers include plastic or glasscontainers, such as glass capillaries having least one dimension ofabout 100 μm to about 1 mm. Suitably, the luminescent nanocrystalscomprise CdSe or ZnS, and can be core/shell nanocrystals comprisingCdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS. Theluminescent nanocrystals can be dispersed in a polymeric matrix. Insuitable embodiments, the hermetically sealed container is spaced apartfrom the LED. In embodiments, the LED devices of the present inventionare white light LED devices.

The present invention also provides display systems comprising a displayand a plurality of the LED devices described herein. Suitably, thedisplay at least partially encloses the light guide. A first portion oflight emitted from the LED is down-converted by the luminescentnanocrystals, and a second portion of light emitted from the LED and thedown-converted light from the luminescent nanocrystals are emitted fromthe light guide and displayed on the display. In exemplary embodiments,the hermetically sealed container is optically coupled to at least twoLEDs.

In a still further embodiment, the present invention provides compositematerials. The composite materials comprise a first polymeric materialhaving a first composition. The composites also comprise a secondpolymeric material having a second composition, and a plurality ofluminescent nanocrystals dispersed in the second polymeric material. Thesecond polymeric material is dispersed in the first polymeric material.

Suitably, the first polymeric material comprises an epoxy or apolycarbonate, and the second polymeric material comprisesaminosilicone. In embodiments, the luminescent nanocrystals emit greenlight and/or red light. Suitably, the luminescent nanocrystals compriseCdSe or ZnS, or can be core/shell luminescent nanocrystals comprisingCdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS. In furtherembodiments, the composites comprising an inorganic layer of SiO₂, TiO₂or AlO₂, hermetically sealing the composite. Suitably, the compositeshave an optical density of about 0.5 to about 0.9 (e.g., about 0.8) atthe blue LED wavelength and a path length of about 50 μm to about 200 μm(e.g., about 100 μm).

The present invention also provides methods of preparing luminescentnanocrystal composite materials. The methods suitably comprisedispersing a plurality of luminescent nanocrystals in a first polymericmaterial to form a mixture of the luminescent nanocrystals and the firstpolymeric material. The mixture is cured, and a particulate is generatedfrom the cured mixture. The particulate is dispersed in a secondpolymeric material to generate the composite material. Suitably, across-linker is added to the mixture prior to the curing. In exemplaryembodiments, the particulate is generated by ball milling the curedmixture. The composites can be formed into a film.

Additional features and advantages of the invention will be set forth inthe description that follows, and in part will be apparent from thedescription, or may be learned by practice of the invention. Theadvantages of the invention will be realized and attained by thestructure and particularly pointed out in the written description andclaims hereof as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate the present invention and, togetherwith the description, further serve to explain the principles of theinvention and to enable a person skilled in the pertinent art to makeand use the invention.

FIG. 1 shows a hermetically sealed luminescent nanocrystal compositionin accordance with one embodiment of the present invention.

FIG. 2 shows a method for hermetically sealing a container comprisingluminescent nanocrystals in accordance with one embodiment of thepresent invention.

FIG. 3 shows hermetically sealed luminescent nanocrystal compositions,including individually sealed compositions, in accordance with oneembodiment of the present invention.

FIG. 4 shows a hermetically sealed container comprising luminescentnanocrystals in accordance with one embodiment of the present invention.

FIG. 5 shows a hermetically sealed composition further comprising amicrolens in accordance with one embodiment of the present invention.

FIGS. 6A-6C show a hermetically sealed composition further comprising alight-focusing apparatus in accordance with one embodiment of thepresent invention.

FIG. 7A shows an LED device in accordance with one embodiment of thepresent invention.

FIG. 7B shows the down-conversion of light from an LED device of thepresent invention.

FIGS. 8A-8C show variations of LED devices of the present invention.

FIG. 9 shows an LED device of the present invention comprisingreflectors.

FIGS. 10A-10B show hermetically sealed capillaries in accordance withembodiments of the present invention.

FIG. 11 shows a display device in accordance with an embodiment of thepresent invention.

FIG. 12 shows a luminescent nanocrystal composite material in accordancewith an embodiment of the present invention.

FIG. 13 shows a flowchart of a method of preparing a luminescentnanocrystal composite material in accordance with an embodiment of thepresent invention.

FIGS. 14A-14B show LED devices comprising a light guide with a region ofnanocrystals in accordance with an embodiment of the present invention.

FIGS. 15A-15C show light intensity output for an LED device comprising alight guide with a region of nanocrystals.

FIGS. 16A-16C show light intensity output for an LED device comprising alight guide with a region of nanocrystals of increasing thickness.

The present invention will now be described with reference to theaccompanying drawings. In the drawings, like reference numbers indicateidentical or functionally similar elements.

DETAILED DESCRIPTION OF THE INVENTION

It should be appreciated that the particular implementations shown anddescribed herein are examples of the invention and are not intended tootherwise limit the scope of the present invention in any way. Indeed,for the sake of brevity, conventional electronics, manufacturing,semiconductor devices, and nanocrystal, nanowire (NW), nanorod,nanotube, and nanoribbon technologies and other functional aspects ofthe systems (and components of the individual operating components ofthe systems) may not be described in detail herein.

The present invention provides various compositions comprisingnanocrystals, including luminescent nanocrystals. The various propertiesof the luminescent nanocrystals, including their absorption properties,emission properties and refractive index properties, can be tailored andadjusted for various applications. As used herein, the term“nanocrystal” refers to nanostructures that are substantiallymonocrystalline. A nanocrystal has at least one region or characteristicdimension with a dimension of less than about 500 nm, and down to on theorder of less than about 1 nm. As used herein, when referring to anynumerical value, “about” means a value of ±10% of the stated value (e.g.“about 100 nm” encompasses a range of sizes from 90 nm to 110 nm,inclusive). The terms “nanocrystal,” “nanodot,” “dot” and “quantum dot”are readily understood by the ordinarily skilled artisan to representlike structures and are used herein interchangeably. The presentinvention also encompasses the use of polycrystalline or amorphousnanocrystals. As used herein, the term “nanocrystal” also encompasses“luminescent nanocrystals.” As used herein, the term “luminescentnanocrystals” means nanocrystals that emit light when excited by anexternal energy source (suitably light). As used herein when describingthe hermetic sealing of nanocrystals, it should be understood that insuitable embodiments, the nanocrystals are luminescent nanocrystals.

Typically, the region of characteristic dimension will be along thesmallest axis of the structure. Nanocrystals can be substantiallyhomogenous in material properties, or in certain embodiments, can beheterogeneous. The optical properties of nanocrystals can be determinedby their particle size, chemical or surface composition. The ability totailor the luminescent nanocrystal size in the range between about 1 nmand about 15 nm enables photoemission coverage in the entire opticalspectrum to offer great versatility in color rendering. Particleencapsulation offers robustness against chemical and UV deterioratingagents.

Nanocrystals, including luminescent nanocrystals, for use in the presentinvention can be produced using any method known to those skilled in theart. Suitable methods and exemplary nanocrystals are disclosed in U.S.Pat. No. 7,374,807; U.S. patent application Ser. No. 10/796,832, filedMar. 10, 2004; U.S. Pat. No. 6,949,206; and U.S. Provisional PatentApplication No. 60/578,236, filed Jun. 8, 2004, the disclosures of eachof which are incorporated by reference herein in their entireties. Thenanocrystals for use in the present invention can be produced from anysuitable material, including an inorganic material, and more suitably aninorganic conductive or semiconductive material. Suitable semiconductormaterials include those disclosed in U.S. patent application Ser. No.10/796,832, and include any type of semiconductor, including groupII-VI, group III-V, group IV-VI and group IV semiconductors. Suitablesemiconductor materials include, but are not limited to, Si, Ge, Sn, Se,Te, B, C (including diamond), P, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN,GaP, GaAs, GaSb, InN, InP, InAs, InSb, AlN, AlP, AlAs, AlSb, GaN, GaP,GaAs, GaSb, ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, BeS,BeSe, BeTe, MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe,PbTe, CuF, CuCl, CuBr, CuI, Si₃N₄, Ge₃N₄, Al₂O₃, (Al, Ga, In)₂ (S, Se,Te)₃, Al₂CO, and an appropriate combination of two or more suchsemiconductors.

In certain aspects, the semiconductor nanocrystals may comprise a dopantfrom the group consisting of: a p-type dopant or an n-type dopant. Thenanocrystals useful in the present invention can also comprise II-VI orIII-V semiconductors. Examples of II-VI or III-V semiconductornanocrystals include any combination of an element from Group II, suchas Zn, Cd and Hg, with any element from Group VI, such as S, Se, Te, Po,of the Periodic Table; and any combination of an element from Group III,such as B, Al, Ga, In, and Tl, with any element from Group V, such as N,P, As, Sb and Bi, of the Periodic Table.

The nanocrystals, including luminescent nanocrystals, useful in thepresent invention can also further comprise ligands conjugated,cooperated, associated or attached to their surface as describedthroughout. Suitable ligands include any group known to those skilled inthe art, including those disclosed in U.S. Pat. Nos. 7,374,807,6,949,206 and U.S. Provisional Patent Application No. 60/578,236, thedisclosures of each of which are incorporated herein by reference. Useof such ligands can enhance the ability of the nanocrystals toincorporate into various solvents and matrixes, including polymers.Increasing the miscibility (i.e., the ability to be mixed withoutseparation) of the nanocrystals in various solvents and matrixes allowsthem to be distributed throughout a polymeric composition such that thenanocrystals do not aggregate together and therefore do not scatterlight. Such ligands are described as “miscibility-enhancing” ligandsherein.

As used herein, the term nanocomposite refers to matrix materialscomprising nanocrystals distributed or embedded therein. Suitable matrixmaterials can be any material known to the ordinarily skilled artisan,including polymeric materials, organic and inorganic oxides.Nanocomposites of the present invention can be layers, encapsulants,coatings or films as described herein. It should be understood that inembodiments of the present invention where reference is made to a layer,polymeric layer, matrix, or nanocomposite, these terms are usedinterchangeably, and the embodiment so described is not limited to anyone type of nanocomposite, but encompasses any matrix material or layerdescribed herein or known in the art.

Down-converting nanocomposites (for example, as disclosed in U.S. Pat.No. 7,374,807) utilize the emission properties of luminescentnanocrystals that are tailored to absorb light of a particularwavelength and then emit at a second wavelength, thereby providingenhanced performance and efficiency of active sources (e.g., LEDs). Asdiscussed above, use of luminescent nanocrystals in such down-conversionapplications, as well as other filtering or coating applications, oftenexposes the nanocrystals to elevated temperatures, high intensity light(e.g., an LED source), external gasses, and moisture. Exposure to theseconditions can reduce the efficiency of the nanocrystals, therebyreducing useful product lifetime. In order to overcome this problem, thepresent invention provides methods for hermetically sealing luminescentnanocrystals, as well as hermetically sealed containers and compositionscomprising luminescent nanocrystals.

Luminescent Nanocrystal Phosphors

While any method known to the ordinarily skilled artisan can be used tocreate nanocrystal phosphors, suitably, a solution-phase colloidalmethod for controlled growth of inorganic nanomaterial phosphors isused. See Alivisatos, A. P., “Semiconductor clusters, nanocrystals, andquantum dots,” Science 271:933 (1996); X. Peng, M. Schlamp, A.Kadavanich, A. P. Alivisatos, “Epitaxial growth of highly luminescentCdSe/CdS Core/Shell nanocrystals with photostability and electronicaccessibility,” J. Am. Chem. Soc. 30:7019-7029 (1997); and C. B. Murray,D. J. Norris, M. G. Bawendi, “Synthesis and characterization of nearlymonodisperse CdE (E=sulfur, selenium, tellurium) semiconductornanocrystallites,” J. Am. Chem. Soc. 115:8706 (1993), the disclosures ofwhich are incorporated by reference herein in their entireties. Thismanufacturing process technology leverages low cost processabilitywithout the need for clean rooms and expensive manufacturing equipment.In these methods, metal precursors that undergo pyrolysis at hightemperature are rapidly injected into a hot solution of organicsurfactant molecules. These precursors break apart at elevatedtemperatures and react to nucleate nanocrystals. After this initialnucleation phase, a growth phase begins by the addition of monomers tothe growing crystal. The result is freestanding crystallinenanoparticles in solution that have an organic surfactant moleculecoating their surface.

Utilizing this approach, synthesis occurs as an initial nucleation eventthat takes place over seconds, followed by crystal growth at elevatedtemperature for several minutes. Parameters such as the temperature,types of surfactants present, precursor materials, and ratios ofsurfactants to monomers can be modified so as to change the nature andprogress of the reaction. The temperature controls the structural phaseof the nucleation event, rate of decomposition of precursors, and rateof growth. The organic surfactant molecules mediate both solubility andcontrol of the nanocrystal shape. The ratio of surfactants to monomer,surfactants to each other, monomers to each other, and the individualconcentrations of monomers strongly influence the kinetics of growth.

In suitable embodiments, CdSe is used as the nanocrystal material, inone example, for visible light down-conversion, due to the relativematurity of the synthesis of this material. Due to the use of a genericsurface chemistry, it is also possible to substitutenon-cadmium-containing nanocrystals.

Core/Shell Luminescent Nanocrystals

In semiconductor nanocrystals, photo-induced emission arises from theband edge states of the nanocrystal. The band-edge emission fromluminescent nanocrystals competes with radiative and non-radiative decaychannels originating from surface electronic states. X. Peng, et al., J.Am. Chem. Soc. 30:7019-7029 (1997). As a result, the presence of surfacedefects such as dangling bonds provide non-radiative recombinationcenters and contribute to lowered emission efficiency. An efficient andpermanent method to passivate and remove the surface trap states is toepitaxially grow an inorganic shell material on the surface of thenanocrystal. X. Peng, et al., J. Am. Chem. Soc. 30:7019-7029 (1997). Theshell material can be chosen such that the electronic levels are type Iwith respect to the core material (e.g., with a larger bandgap toprovide a potential step localizing the electron and hole to the core).As a result, the probability of non-radiative recombination can bereduced.

Core-shell structures are obtained by adding organometallic precursorscontaining the shell materials to a reaction mixture containing the corenanocrystal. In this case, rather than a nucleation-event followed bygrowth, the cores act as the nuclei, and the shells grow from theirsurface. The temperature of the reaction is kept low to favor theaddition of shell material monomers to the core surface, whilepreventing independent nucleation of nanocrystals of the shellmaterials. Surfactants in the reaction mixture are present to direct thecontrolled growth of shell material and ensure solubility. A uniform andepitaxially grown shell is obtained when there is a low lattice mismatchbetween the two materials.

Exemplary materials for preparing core-shell luminescent nanocrystalsinclude, but are not limited to, Si, Ge, Sn, Se, Te, B, C (includingdiamond), P, Co, Au, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs,GaSb, InN, InP, InAs, InSb, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb,ZnO, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe,MgS, MgSe, GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, PbTe, CuF,CuCl, CuBr, CuI, Si₃N₄, Ge₃N₄, Al₂O₃, (Al, Ga, In)₂ (S, Se, Te)₃, Al₂CO,and an appropriate combination of two or more such materials. Exemplarycore-shell luminescent nanocrystals for use in the practice of thepresent invention include, but are not limited to, (represented asCore/Shell), CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS, CdTe/ZnS,as well as others.

Hermetically Sealed Luminescent Nanocrystal Compositions and LuminescentNanocrystal-Comprising Containers

In one embodiment, the present invention provides methods ofhermetically sealing a composition comprising a plurality of luminescentnanocrystals. The methods suitably comprise disposing a barrier layer onthe composition to seal the luminescent nanocrystals. As discussedthroughout, the terms “hermetic,” “hermetic sealing,” and “hermeticallysealed” are used throughout to indicate that the composition, containerand/or luminescent nanocrystals are prepared in such a way that thequantity of gases (e.g., air) or moisture that passes through orpenetrates the container or composition, and/or that contacts theluminescent nanocrystals is reduced to a level where it does notsubstantially effect the performance of the nanocrystals (e.g., theirluminescence). Therefore, a “hermetically sealed composition,” forexample one that comprises luminescent nanocrystals, is a compositionthat does not allow an amount of air (or other gas, liquid or moisture)to penetrate the composition and contact the luminescent nanocrystalssuch that the performance of the nanocrystals (e.g., the luminescence)is substantially effected or impacted (e.g., reduced).

As used throughout, a plurality of luminescent nanocrystals means morethan one nanocrystal (i.e., 2, 3, 4, 5, 10, 100, 1,000, 1,000,000, etc.,nanocrystals). The compositions will suitably comprise luminescentnanocrystals having the same composition, though in further embodiments,the plurality of luminescent nanocrystals can be various differentcompositions. For example, the luminescent nanocrystals can all emit atthe same wavelength, or in further embodiments, the compositions cancomprise luminescent nanocrystals that emit at different wavelengths.

As shown in FIG. 1, in one embodiment, the present invention provides acomposition 100 comprising a plurality of luminescent nanocrystals 104.Any nanocrystal can be prepared in the compositions of the presentinvention, including those described throughout, and otherwise known inthe art, for example, as disclosed in U.S. Pat. No. 7,374,807.

In suitable embodiments, composition 100 comprises a plurality ofluminescent nanocrystals 104 dispersed throughout a matrix 102. As usedthroughout, dispersed includes uniform (i.e., substantially homogeneous)as well as non-uniform (i.e., substantially heterogeneous)distribution/placement of nanocrystals. Suitable matrixes for use in thecompositions of the present invention include polymers and organic andinorganic oxides. Suitable polymers for use in the matrixes of thepresent invention include any polymer known to the ordinarily skilledartisan that can be used for such a purpose. In suitable embodiments,the polymer will be substantially translucent or substantiallytransparent. Such polymers include, but are not limited to, poly(vinylbutyral):poly(vinyl acetate); epoxies; urethanes; silicone andderivatives of silicone, including, but not limited to,polyphenylmethylsiloxane, polyphenylalkylsiloxane, polydiphenylsiloxane,polydialkylsiloxane, fluorinated silicones and vinyl and hydridesubstituted silicones; acrylic polymers and copolymers formed frommonomers including but not limited to, methylmethacrylate,butylmethacrylate and laurylmethacrylate; styrene based polymers; andpolymers that are crosslinked with difunctional monomers, such asdivinylbenzene.

The luminescent nanocrystals used the present invention can be embeddedin a polymeric (or other suitable material, e.g., waxes, oils) matrixusing any suitable method, for example, mixing the nanocrystals in apolymer and casting a film, mixing the nanocrystals with monomers andpolymerizing them together, mixing the nanocrystals in a sol-gel to forman oxide, or any other method known to those skilled in the art. As usedherein, the term “embedded” is used to indicate that the luminescentnanocrystals are enclosed or encased within the polymer that makes upthe majority component of the matrix. It should be noted thatluminescent nanocrystals are suitably uniformly distributed throughoutthe matrix, though in further embodiments they can be distributedaccording to an application-specific uniformity distribution function.

The thickness of the composition of the present invention can becontrolled by any method known in the art, such as spin coating andscreen printing. The luminescent nanocrystal compositions of the presentinvention can be any desirable size, shape, configuration and thickness.For example, the compositions can be in the form of layers, as well asother shapes, for example, discs, spheres, cubes or blocks, tubularconfigurations and the like. While the various compositions of thepresent invention can be any thickness required or desired, suitably,the compositions are on the order of about 100 mm in thickness (i.e., inone dimension), and down to on the order of less than about 1 mm inthickness. In other embodiments, the polymeric layers of the presentinvention can be on the order of 10's to 100's of microns in thickness.The luminescent nanocrystals can be embedded in the variouscompositions/matrixes at any loading ratio that is appropriate for thedesired function. Suitably, the luminescent nanocrystals will be loadedat a ratio of between about 0.001% and about 75% by volume dependingupon the application, matrix and type of nanocrystals used. Theappropriate loading ratios can readily be determined by the ordinarilyskilled artisan and are described herein further with regard to specificapplications. In exemplary embodiments the amount of nanocrystals loadedin a luminescent nanocrystal composition are on the order of about 10%by volume, to parts-per-million (ppm) levels.

Luminescent nanocrystals for use in the present invention will suitablybe less than about 100 nm in size, and down to less than about 2 nm insize. In suitable embodiments, the luminescent nanocrystals of thepresent invention absorb visible light. As used herein, visible light iselectromagnetic radiation with wavelengths between about 380 and about780 nanometers that is visible to the human eye. Visible light can beseparated into the various colors of the spectrum, such as red, orange,yellow, green, blue, indigo and violet. The photon-filteringnanocomposites of the present invention can be constructed so as toabsorb light that makes up any one or more of these colors. For example,the nanocomposites of the present invention can be constructed so as toabsorb blue light, red light, or green light, combinations of suchcolors, or any colors in between. As used herein, blue light compriseslight between about 435 nm and about 500 nm, green light comprises lightbetween about 520 nm and 565 nm and red light comprises light betweenabout 625 nm and about 740 nm in wavelength. The ordinarily skilledartisan will be able to construct nanocomposites that can filter anycombination of these wavelengths, or wavelengths between these colors,and such nanocomposites are embodied by the present invention.

In other embodiments, the luminescent nanocrystals have a size and acomposition such that they absorb photons that are in the ultraviolet,near-infrared, and/or infrared spectra. As used herein, the ultravioletspectrum comprises light between about 100 nm to about 400 nm, thenear-infrared spectrum comprises light between about 750 nm to about 100μm in wavelength and the infrared spectrum comprises light between about750 nm to about 300 μm in wavelength.

While luminescent nanocrystals of any suitable material can be used inthe practice of the present invention, in certain embodiments, thenanocrystals can be ZnS, InAs or CdSe nanocrystals, or the nanocrystalscan comprise various combinations to form a population of nanocrystalsfor use in the practice of the present invention. As discussed above, infurther embodiments, the luminescent nanocrystals are core/shellnanocrystals, such as CdSe/ZnS, CdSe/CdS or InP/ZnS.

In order to hermetically seal the compositions of the present invention,a barrier layer is disposed on the composition. For example, as shown inFIG. 1, a barrier layer 106 is disposed on the matrix 102 comprisingluminescent nanocrystals 104, thereby generating a hermetically sealedcomposition. The term “barrier layer” is used throughout to indicate alayer, coating, sealant or other material that is disposed on the matrix102 so as to hermetically seal the composition. Examples of barrierlayers include any material layer, coating or substance that can createan airtight seal on the composition. Suitable barrier layers includeinorganic layers, suitably an inorganic oxide such as an oxide of Al,Ba, Ca, Mg, Ni, Si, Ti or Zr. Exemplary inorganic oxide layers, includeSiO₂, TiO₂, AlO₂ and the like. As used throughout, the terms “dispose,”and “disposing” include any suitably method of application of a barrierlayer. For example, disposing includes layering, coating, spraying,sputtering, plasma enhanced chemical vapor deposition, atomic layerdeposition, or other suitable method of applying a barrier layer to thecompositions. In suitable embodiments, sputtering is used to dispose thebarrier layer on the compositions. Sputtering comprises a physical vapordeposition process where high-energy ions are used to bombard elementalsources of material, which eject vapors of atoms that are then depositedin thin layers on a substrate. See for example, U.S. Pat. Nos.6,541,790; 6,107,105; and 5,667,650, the disclosures of each of whichare incorporated by reference herein in their entireties.

In further embodiments, disposing the barrier layer can be carried outusing atomic layer deposition. In applications such as coatings of LEDs,luminescent nanocrystal compositions, such as nanocrystal-comprisingpolymeric layers, can often have complex geometries and features. Forexample, components of the LED such as bond wires and solder jointsoften are directly in contact with, or even contained within, thepolymeric layer. In order to properly hermetically seal the nanocrystalcomposition, a virtually defect-free (i.e., pin hole-free) barrier layeris often required. In addition, application of the barrier layer shouldnot degrade the polymer or the nanocrystals. Therefore, in suitableembodiments, atomic layer deposition is used to dispose the barrierlayer.

Atomic layer deposition (ALD) can comprise disposition of an oxide layer(e.g., TiO₂, SiO₂, AlO₂, etc.) on the luminescent nanocrystalcomposition, or in further embodiments, deposition of a non-conductivelayer, such as a nitride (e.g., silicon nitride) can be used. ALDdeposits an atomic layer (i.e., only a few molecules thick) byalternately supplying a reaction gas and a purging gas. A thin coatinghaving a high aspect ratio, uniformity in a depression, and goodelectrical and physical properties, can be formed. Barrier layersdeposited by the ALD method suitably have a low impurity density and athickness of less than 1000 nm, suitably less than about 500 nm, lessthan about 200 nm, less than about 50 nm, less than about 20 nm, or lessthan about 5 nm.

For example, in suitable embodiments, two reaction gases, A and B areused. When only the reaction gas, A, flows into a reaction chamber,atoms of the reaction gas A are chemically adsorbed on the luminescentnanocrystal composition. Then, any remaining reaction gas A is purgedwith an inert gas such as Ar or nitrogen. Then, reaction gas B flows in,wherein a chemical reaction between the reaction gases A and B occursonly on the surface of the luminescent nanocrystal composition on whichthe reaction gas A has been adsorbed, resulting in an atomic barrierlayer on the composition.

In embodiments where a non-conductive layer, such as a nitride layer isdisposed, suitably SiH₂Cl₂ and remote plasma enhanced NH₃ are used todispose a silicon nitride layer. This can be performed at a lowtemperature and does not require the use of reactive oxygen species.

Use of ALD for disposition of a barrier layer on the luminescentnanocrystal composition generates a virtually pin-hole free barrierlayer regardless of the morphology of the substrate. The thickness ofthe barrier layer can be increased by repeating the deposition steps,thereby increasing the thickness of the layer in atomic layer unitsaccording to the number of repetitions. In addition, the barrier layercan be further coated with additional layers (e.g., via sputtering, CVDor ALD) to protect or further enhance the barrier.

Suitably, the ALD methods utilized in the practice of the presentinvention are performed at a temperature of below about 500° C.,suitably below about 400° C., below about 300° C., or below about 200°C.

Exemplary barrier materials include organic material designed tospecifically reduce oxygen and moisture transmission. Examples includefilled epoxies (such as alumina filled epoxies) as well as liquidcrystalline polymers.

As discussed throughout, matrix 102 suitably comprises a polymericsubstrate. Thus, the present invention comprises methods of hermeticallysealing compositions comprising luminescent nanocrystals, suitablypolymeric substrates comprising luminescent nanocrystals, by disposing abarrier layer on the composition using any of the various methodsdisclosed herein or otherwise known in the art.

The ability to use polymeric substrates as matrix 102 allows for theformation of various shapes and configurations of the compositions,simply by molding or otherwise manipulating the compositions into thedesired shape/orientation. For example, a solution/suspension ofluminescent nanocrystals can be prepared (e.g., luminescent nanocrystalsin a polymeric matrix). This solution can then be placed into anydesired mold to form a required shape, and then cured (e.g., cooled orheated depending upon the type of polymer) to form a solid or semi-solidstructure. For example, a mold can be prepared in the shape of a cap ordisc to place on or over an LED. This then allows for preparation of acomposition that can be used as a down-converting layer, for example.Following preparation of the desired shape, a barrier layer is thendisposed on the composition to hermetically seal the composition,thereby protecting the luminescent nanocrystals from oxidation.

In additional embodiments, a composition comprising luminescentnanocrystals (e.g., a polymeric composition) can be disposed directly ona desired substrate or article (for example an LED). The luminescentnanocrystal composition (e.g., a solution or suspension) can then becured and then a barrier layer disposed on the composition, therebyhermetically sealing the composition directly on the desired substrateor article. Such embodiments therefore do not require the preparation ofa separate composition, and instead allow for the preparation of thecomposition directly on the desired article/substrate (e.g., a lightsource or other end product).

In a further embodiment, the present invention provides methods forhermetically sealing a container which comprises a plurality ofluminescent nanocrystals. Suitably the methods comprise providing acontainer, introducing luminescent nanocrystals into the container, andthen sealing the container. For example, an exemplary method forhermetically sealing a container of luminescent nanocrystals is shown inflowchart 200 of FIG. 2, with reference to FIGS. 3 and 4. In step 202 ifFIG. 2, a container is provided, for example, containers 302 or 402 inFIGS. 3 and 4 are be provided. As used herein, “container” refers to anysuitable article or receptacle for retaining nanocrystals. It should beunderstood that, as used herein, a “container” comprising luminescentnanocrystals and a “composition” comprising luminescent nanocrystalsrepresent different embodiments of the present invention. A“composition” comprising luminescent nanocrystals refers to a matrix,e.g., a polymer substrate, solution or suspension, which containsnanocrystals dispersed throughout. A “container” as used herein, refersto a carrier, receptacle or pre-formed article into which luminescentnanocrystals are introduced (often a composition of luminescentnanocrystals, e.g., a polymeric matrix comprising luminescentnanocrystals). Examples of containers include, but are not limited to,polymeric or glass structures such as tubes, molded or formed vessels,or receptacles. In exemplary embodiments, a container can be formed byextruding a polymeric or glass substance into a desired shape, such as atube (circular, rectangular, triangular, oval or other desiredcross-section), or similar structure. Any polymer can be used to formthe containers for use in the practice of the present invention,including those described throughout. Exemplary polymers for preparationof containers for use in the practice of the present invention include,but are not limited to, acrylics, poly(methyl methacrylate) (PMMA), andvarious silicone derivatives. Additional materials can also be used toform the containers for use in the practice of the present invention.For example, the containers can be prepared from metals, variousglasses, ceramics and the like.

For example, as shown in FIG. 2, once a container is provided in step202, a plurality of luminescent nanocrystals 104 are then introducedinto the container in step 204. As used herein, “introduced” includesany suitable method of providing luminescent nanocrystals into acontainer. For example, luminescent nanocrystals can be injected into acontainer, placed into a container, drawn into a container (e.g., byusing a suction or vacuum mechanism), directed into a container, forexample by using an electromagnetic field, or other suitable method forintroducing luminescent nanocrystals into a container. Suitably, theluminescent nanocrystals are present in a solution or suspension, forexample in a polymeric solution, thereby aiding in the introduction ofthe nanocrystals into the container. In exemplary embodiments,luminescent nanocrystals 104 can be drawn into a container, for examplea tubular container 302, such as is shown in FIG. 3. In furtherembodiments, as shown in FIG. 4, a container 402 can be prepared with acavity or void 404 into which luminescent nanocrystals 104 can beintroduced. For example, a solution of luminescent nanocrystals 104 canbe introduced into the cavity 404 in container 402.

Following introduction of the luminescent nanocrystals into thecontainer, the container is then hermetically sealed, as shown in FIG.2, in step 206. Examples of methods for hermetically sealing thecontainer include, but are not limited to, heat sealing the container,ultrasonic welding the container, soldering the container or adhesivebonding the container. For example, as shown in FIG. 3, container 302can be sealed at any number of positions, creating various number ofseals 304 throughout the container. In exemplary embodiments, container302 can be heat sealed at various positions throughout the container,for example by heating and then “pinching” the container at varioussealing points (304).

In suitable embodiments, as shown in FIG. 3, a polymeric or glass tubecan be used as container 302. A solution of luminescent nanocrystals 104can then be drawn into the container by simply applying a reducedpressure to an end of the container. Container 302 can then be sealed byheating and “pinching” the container at various sealing positions orseals 304 throughout the length of the container, or by using othersealing mechanisms as described throughout. In this way, container 302can be separated into various individual sections 306. These sectionscan either retained together as a single, sealed container 308, or thesections can be separated into individual pieces, as shown in FIG. 3.Hermetic sealing of container 302 can be performed such that eachindividual seal 304 separates solutions of the same nanocrystals. Inother embodiments, seals 304 can be created such that separate sectionsof container 302 each contain a different nanocrystal solution (i.e.,different nanocrystal composition, size or density).

In a further embodiment, as shown in FIG. 4, luminescent nanocrystalscan be placed into a cavity/void 404 formed in container 402. Container402 can be produced using any suitable process. For example, container402 can be injection molded into any desired shape or configuration.Cavity/void 404 can be prepared during the initial preparation process(i.e., during molding) or can be subsequently added after formation.Luminescent nanocrystals 104 are then introduced into cavity/void 404.For example, luminescent nanocrystals can be injected or placed intocavity/void 404 of container 402. Suitably, a solution of luminescentnanocrystals will fill the entire container, though it is not necessaryto completely fill the container with nanocrystals. In the case wherethe entire container is not filled, it is necessary though to removesubstantially all of the air in the container prior to sealing to ensurethat the luminescent nanocrystals are hermetically sealed. As shown inFIG. 4, in exemplary embodiments, container 402 can be hermeticallysealed by bonding, welding or otherwise sealing the container with acover or lid 406. Suitably, cover 406 is produced from the same materialas container 402 (and can suitably be partially attached prior tosealing), though it can also comprise a different material. Inadditional embodiments, a material such as an organic material designedto specifically reduce oxygen and moisture transmission can be used tocover or seal container 402. Examples include filled epoxies (such asalumina filled epoxies) as well as liquid crystalline polymers.

The ability to produce custom designed containers, for example viamolding, extruding or otherwise shaping containers, allows forpreparation of very specialized parts into which luminescentnanocrystals can be introduced and hermetically sealed. For example,shapes can be produced that conform around LEDs or other light sources(e.g., for use to pipe down-conversion into another optical component).In addition, various films, discs, layers, and other shapes can beprepared. In exemplary embodiments, several different containers can beprepared, each of which can contain different compositions ofluminescent nanocrystals (i.e., each composition emitting a differentcolor), and then the separate containers can be utilized together tocreate the desired performance characteristics. In further embodiments,containers can be prepared with multiple cavities or reservoirs intowhich luminescent nanocrystals can be introduced.

While luminescent nanocrystals 104 can be hermetically sealed intocontainers 302, 402, while still in solution, suitably the luminescentnanocrystal solution is cured before hermetic sealing (e.g., in step 210of FIG. 2). As used herein, “cured” refers to the process of hardening asolution of luminescent nanocrystals (e.g., a polymeric solution).Curing can be achieved by simply allowing the solution to dry and anysolvent to evaporate, or curing can be achieve by heating or exposingthe solution to light or other external energy. Following curing, thecontainer can be hermetically sealed using the various methods describedthroughout.

In exemplary embodiments, no additional hermetic sealing is necessary toprotect the luminescent nanocrystals from oxidative degradation. Forexample, sealing luminescent nanocrystals in a glass or polymericcontainer provides sufficient protection from oxygen and moisture thatfurther modifications are not necessary. However, in furtherembodiments, an additional level of protection from oxidation can beadded to the hermetically sealed containers by disposing a barrier layeron the container. For example, as shown in step 208 of FIG. 2. Asdescribed throughout, exemplary barrier layers include inorganic layers,such as inorganic oxides like SiO₂, TiO₂ and AlO₂, as well as organicmaterials. While any method of disposing the barrier layer onto thecontainer can be used, suitably the barrier layer is sputtered onto thecontainer or disposed onto the container via ALD. As shown in FIG. 3,barrier layer 106 can be disposed on the container with sealed sections,or on individual sections following sealing and separation from oneanother, thereby producing hermetically sealed containers (310, 312).

In suitable embodiments of the present invention, the various steps toproduce a hermetically sealed container of luminescent nanocrystals areperformed in an inert atmosphere. For example, steps 204, 206 and 208(and 210 if required) are all suitably performed in an inert atmosphere,i.e., either in a vacuum and/or with only N₂ or other inert gas(es)present.

In further embodiments, the present invention provides hermeticallysealed compositions and containers comprising a plurality of luminescentnanocrystals. In exemplary embodiments, the luminescent nanocrystalscomprise one or more semiconductor materials (as described throughout),and are suitably core/shell luminescent nanocrystals, such as CdSe/ZnS,CdSe/CdS or InP/ZnS. In general, the luminescent nanocrystals are of asize of between about 1-50 nm, suitably about 1-30 nm, more suitablyabout 1-10 nm, e.g., about 3-9 nm. In exemplary embodiments, asdescribed throughout, the hermetically sealed compositions andcontainers of the present invention comprise a barrier layer coating thecomposition (e.g., barrier layer 106 coating composition 100 in FIG. 1)and optionally comprise a barrier layer coating the containers (e.g.,barrier layer 106 coating container 302 in FIG. 3). Exemplary types ofbarrier layers include those described throughout, such as inorganiclayers like SiO₂, TiO₂, and AlO₂.

In addition to generating various shapes, orientations and sizes ofcontainers for hermetically sealing the luminescent nanocrystals,additional modifications can also be made to thecontainers/compositions. For example, the containers/compositions can beprepared in the shape of a lens for filtration or other modification ofa light source. In further embodiments, the containers/compositions canbe modified, for example, by preparing or attaching a reflector orsimilar apparatus to the containers/compositions.

Additionally, micropatterns can be molded directly into the compositionsor containers to form flat (or curved) microlenses. This can be doneduring the molding process or in a subsequent embossing step.Micropatterns are often utilized to make flat microlenses when limitedspace is available, such as in displays. Examples of this technologyinclude the brightness enhancing films from 3M corporation that have 20to 50 micron prisms molded into their surface. In suitable embodiments,the present invention provides microlenses comprising luminescentnanocrystals hermetically sealed in an encapsulating polymer (or in acontainer) which is then micropatterned such that a microlens is formed.For example, as shown in FIG. 5, microlens assembly 500 suitablycomprises hermetically sealed composition 502 comprising a layer 504 ofluminescent nanocrystals 104 placed on top of, or otherwise in contactwith, LED 506 which is supported by substrate 508. The surface ofcomposition 502 can be molded into various shapes, for example toinclude a series of microprisms 510, as shown in FIG. 5, thereby formingthe microlens.

In exemplary embodiments, use of a microlens in combination with thehermetically sealed compositions of the present invention allow for anincrease in the amount of emitted light captured (and therefore emittedfrom the composition) from the LED/luminescent nanocrystals. Forexample, the addition of microprisms or other microlens assembly to thehermetically sealed compositions and containers of the present inventionsuitably leads to an increase in the amount of light captured of greaterthan about 10% (e.g., about 10-60%, about 10-50%, about 10-40%, about20%-40%, or about 30-40%) as compared to a composition that does notcomprise microprisms or other microlens assembly. This increase in theamount of light captured correlates directly to an increase in the totalamount of light that is emitted from the composition or container.

In suitable embodiments, a dichroic mirror can be attached or otherwiseassociated with the containers/compositions that forms a lens forapplication over a light source. A dichroic mirror allows a particularwavelength of light to pass through the mirror, while reflecting others.As light from the source enters the lens-shaped containers/compositions,the photons are able to enter the containers/compositions and excite thevarious luminescent nanocrystals that have been hermetically sealedinside. As the luminescent nanocrystals emit light, photons are able toexit the containers/compositions, but not reflect back toward theinitial light source (as they are reflected by the dichroic mirror). Inembodiments then, suitable containers/compositions can be created to fitover a light source (e.g., an LED). This allows light to enter from thesource and excite the luminescent nanocrystals inside, but emitted lightis only allowed to exit the containers/compositions away from the lightsource, blocked from reflecting back into the source by the dichroicmirror. For example, blue light from an LED source is allowed to passthrough the dichroic mirror and excite encapsulated luminescentnanocrystals, which then emit green light. The green light is reflectedby the mirror and not allowed to reflect back into the light source.

As discussed herein, in suitable embodiments the hermetically sealedluminescent nanocrystal compositions of the present invention are usedin combination with an LED or other light source. Applications for thesesealed nanocrystal/LEDs are well known to those of ordinary skill in theart, and include the following. For example, such sealednanocrystal/LEDs can be used in microprojectors (see, e.g., U.S. Pat.Nos. 7,180,566 and 6,755,563, the disclosures of which are incorporatedby reference herein in their entireties); in applications such ascellular telephones; personal digital assistants (PDAs); personal mediaplayers; gaming devices; laptops; digital versatile disk (DVD) playersand other video output devices; personal color eyewear; and head-up orhead-down (and other) displays for automobiles and airplanes. Inadditional embodiments, the hermetically sealed nanocrystals can be usedin applications such as digital light processor (DLP) projectors.

In additional embodiments, the hermetically sealed compositions andcontainers disclosed throughout can be used to minimize the property ofan optical system known as etendue (or how spread out the light is inarea and angle). By disposing, layering or otherwise covering (evenpartially covering) an LED or other light source with a composition orcontainer of the presently claimed invention, and controlling the ratioof the overall area (e.g, the thickness) of the luminescent nanocrystalcomposition or container to the area (e.g., the thickness) of the LED,the amount or extent of etendue can be minimized, thereby increasing theamount of light captured and emitted. Suitably, the thickness of theluminescent nanocrystal composition or container will be less than about⅕ the thickness of the LED layer. For example, the luminescentnanocrystal composition or container will be less than about ⅙, lessthan about 1/7, less than about ⅛, less than about 1/9, less than about1/10, less than about 1/15 or less than about 1/20 of the thickness ofthe LED layer.

In further embodiments, the hermetically sealed luminescent nanocrystalsof the presently claimed invention can be used in a system 602comprising a light-focusing apparatus (or focusing apparatus) 604, forexample, as shown in FIGS. 6A-6C. In exemplary embodiments, alight-focusing apparatus 604 is prepared and attached or otherwiseassociated with an LED 506. Suitably, light-focusing apparatus 604 is inthe shape of a cube or rectangular box, where the bottom of the boxsituated on or above the LED 506, with the sides of the apparatusextending above the LED. FIG. 6A shows a cross sectional view ofapparatus 604, taken through plane 1-1 of FIG. 6B, showing a top view ofthe apparatus 604, LED 506 and substrate 508. In exemplary embodiments,apparatus 604 comprises four sides surrounding LED 506, though in otherembodiments any number of sides can be used (e.g., 2, 3, 4 5, 6, 7, 8,9, 10, etc.), or a circular apparatus can be used, such that only asingle piece (or multiple pieces fashioned for form a continuous piece)of material surrounds LED 506. In general, the top and bottom oflight-focusing apparatus 604 are open (i.e., the apparatus is placeddirectly on top of and encloses LED 506), though in other embodiments,either the top or bottom, or both, of apparatus 604 can be closed by anadditional piece of material.

Focusing apparatus 604 suitably is made of a material that can reflectlight that is generated by LED, or is coated with a material thatreflects light. For example, focusing apparatus can comprise a polymer,metal, ceramic, etc. In other embodiments, the inner surface (i.e., thesurface facing LED) can be coated with a reflective material such as ametal (e.g, Al) or other reflective coating. This reflective coating canbe deposited on the surfaces of focusing apparatus using any suitablemethod, such as spray coating, ALD, painting, dipping, spin coating,etc.

Focusing apparatus 604 suitably encloses or encapsulates a hermeticallysealed nanocrystal composition 504 (or hermetically sealed nanocrystalcontainer) of the present invention, and thus the apparatus isassociated with the composition or container. In suitable embodiments,focusing apparatus 604 can be prepared separately from LED 506 and thenattached to the LED, for example by an adhesive such as an epoxy, andthen the center portion of the apparatus 604 filled in with ahermetically sealed nanocrystal composition 504. In further embodiments,focusing apparatus 604 can be directly assembled on LED 506. In otherembodiments, a hermetically sealed composition can be disposed on LEDand then focusing apparatus can be added, either as a pre-madeapparatus, or constructed directly on the LED. In suitable embodiments,apparatus 604 also comprises a cover (e.g., a glass or polymer cover) toseal the nanocrystal composition 504. Such a cover can act as a hermeticseal over the nanocrystal composition, or simply as an additionalstructural element to support the nanocrystal composition and thefocusing apparatus. Such a cover can be placed directly on top ofnanocrystal composition 504, or can be placed at the top of apparatus604, or in any position in between.

As shown in FIGS. 6A and 6C, in suitable embodiments, focusing apparatus604 is prepared in such a manner that the sides of the apparatus taperinward at the bottom (e.g., near the LED), but outward at the top (awayfrom the LED). This helps to aid in gathering and focusing the light 606into a beam so as to direct the light out of the apparatus. As shownFIG. 6C, suitably focusing apparatus 604 directs light 606 out from theLED. By using tapered or angled sides, light 606 that is emitted fromthe LED/nanocrystals is directed out of the apparatus 604, rather thanlost either by bouncing back and forth inside of the apparatus, or lostsimply unable to escape. Use of light-focusing apparatus in combinationwith the luminescent nanocrystal compositions and containers of thepresent invention can suitably be employed in microprojectors and otherapplications where a focus, beam of light is desired or required.

Light-Emitting Diode (LED) Devices with Hermetically Sealed Nanocrystals

In a further embodiment, the present invention comprises light-emittingdiode (LED) devices. An exemplary LED device 700 is shown in FIG. 7A.LED device 700 suitably comprises an LED 702. LED 702 is shown onsubstrate 706 for illustrative purposes only. It should be understoodthat any suitable configuration of an LED can be utilized in thepractice of the present invention. In addition, multiple (i.e., morethan one) LED can be utilized in LED device 700. LED device 700 furthercomprises a hermetically sealed container 708 comprising a plurality ofluminescent nanocrystals 710. Container 708 is optically coupled to LED702. LED device 700 also comprises a light guide 712 optically coupledto hermetically sealed container 708.

In embodiments of the present invention, a first portion of lightemitted from the LED is down-converted by the luminescent nanocrystals710. A second portion of light emitted from the LED and thedown-converted light from the luminescent nanocrystals are emitted fromlight guide 712.

Any suitable LED can be utilized in the LED devices of the presentinvention, including various configurations of LEDs, and LEDs emittinglight over the entire visible spectrum, as well as LEDs that emitultraviolet light (light with a wavelength of 10 nm to about 380 nm).Suitably, LED 702 emits blue light. As described herein, the visiblespectrum includes light having wavelengths between about 380 nm andabout 780 nm that is visible to the human eye. Visible light can beseparated into the various colors of the spectrum, such as red, orange,yellow, green, blue, indigo and violet. As used herein, blue lightcomprises light between about 435 nm and about 500 nm, green lightcomprises light between about 520 nm and 565 nm, more suitably about 525nm to about 530 nm, and red light comprises light between about 625 nmand about 740 nm in wavelength, more suitably about 625 nm to about 640nm.

Suitably, as shown in FIG. 7B, LED 702 emits blue light 716. A firstportion 718 of the blue light emitted from the LED is down-converted byluminescent nanocrystals 710. As the nanocrystals absorb this portion ofblue light and then emit light at a second wavelength 722, 724 (see FIG.7B). Suitably, the light emitted from nanocrystals 710 comprises lighthaving wavelengths primarily in the green (e.g, between about 520 nm and565 nm, more suitably about 525 nm to about 530 nm) and red (e.g,between about 625 nm and about 740 nm in wavelength, more suitably about625 nm to about 640 nm) ranges. Thus, suitably nanocrystals 710 comprisetwo populations of nanocrystals. One population of nanocrystals isdesigned to absorb blue light and emit red light, and a secondpopulation of nanocrystals is designed to absorb blue light and emitgreen light. The populations of nanocrystals suitably comprise aplurality (i.e., 2 or more, 10 or more, 100 or more 1000 or more, etc.)of nanocrystals. As described herein, the ability to tailor thecomposition and size of the nanocrystals allows for the design ofnanocrystals having specific absorption and emission characteristics.

“A first portion” of blue light 718 refers to a percentage of the bluelight 716 emitted from LED that is down-converted from blue to anotherwavelength(s) of light. A first portion can be any amount of theoriginal blue light 716 emitted from LED 702 that is less than the totalamount of blue light given off by the LED (e.g., about 99% to about 1%of the blue light emitted from LED 702, suitably about 80% to about 30%,about 70% to about 40%, about 70% to about 50% or about 60%).

A second portion 720 of blue light emitted from LED 702 passes throughhermetically sealed container 708, emerging as blue light (suitablyabout 20% to about 50%, or about 20% to about 40%). This second portionof blue light 720 and the down-converted light 722 and 724 emitted fromthe nanocrystals (e.g., red light and green light) are then emitted 726from the light guide 712. The blue light emitted from the LED 720, andthe down-converted green light and red light (722 and 724) suitablycombine to produce white light 726 when ultimately emitted from thelight guide.

In further embodiments, two (or more) blue light emitting LEDs can beutilized, so that all of the light from one (or more) LED isdown-converted by the nanocrystals, while all of the light from thesecond (third, etc.) LED passes through the hermetically sealedcontainer, resulting in the red, green and blue wavelengths that combineto produce white light.

Hermetically sealed container 708 is suitably a plastic or glasscontainer. Exemplary hermetically sealed containers are describedthroughout. In suitable embodiments, the hermetically sealed containeris a plastic or glass (e.g., borosilicate) capillary. As used herein“capillary” refers to an elongated container having a length dimensionthat is longer than both its width and height dimension. Suitably, acapillary is a tube or similar structure having a circular, rectangular,square, triangular, irregular, or other cross-section. Suitably, acapillary for use in the LED devices of the present invention can beconfigured so as to match the shape and orientation of the LED to whichit is optically coupled. In exemplary embodiments, a capillary has atleast one dimension of about 100 μm to about 1 mm. In embodiments inwhich a plastic capillary it utilized, a coating such as SiO₂, AlO₂ orTiO₂, as well as others described herein, can be added so as to providean additional hermetic seal to the capillary.

Suitably, a capillary of the present invention has a thickness of about50 μm to about 10 mm, about 100 μm to about 1 mm, or about 100 μm toabout 500 μm. Thickness refers to dimension of the capillary into theplane of the light guide. Suitably, a capillary of the present inventionhas a height (in the plane of the light guide) of about 50 μm to about10 mm, about 100 μm to about 1 mm, or about 100 μm to about 500 μm.Suitably, a capillary of the present invention has a length (in theplane of the light guide) of about 1 mm to about 50 mm, about 1 mm toabout 40 mm about 1 mm to about 30 mm about 1 mm to about 20 mm about 1mm to about 10 mm.

In still further embodiments a hermetically sealed composition ofluminescent nanocrystals as described herein can be utilized in the LEDdevices. In such embodiments, the hermetically sealed composition isoptically coupled to the LED and the light guide, and thus provides thedown-converted light from the nanocrystals.

As used herein a “light guide” refers to an optical component that issuitable for directing electromagnetic radiation (light) from oneposition to another. Exemplary light guides include fiber optic cables,polymeric or glass solid bodies such as plates, films, containers, orother structures. The size of the light guide will depend on theultimate application and characteristics of the LED devices. In general,the thickness of the light guide will be compatible with thickness ofthe LED. The other dimensions of the light guide are generally designedto extend beyond the dimensions of the LED, and are suitably on theorder of 10s of millimeters, to 10s to 100s of centimeters. While thelight guides illustrated in the Figures represent embodiments suitablefor use in display systems and the like, other light guides, includingfiber optic cables, etc., can also be utilized.

Exemplary nanocrystals for use in the practice of the present inventionare described herein. In suitable embodiments, the nanocrystals arecore/shell nanocrystals. Suitably, the nanocrystals contain one or moreligands attached to their surface that increase the solubility of thenanocrystals in a polymeric material. Exemplary ligands are describedherein and in U.S. Pat. Nos. 7,374,807, 6,949,206 and U.S. ProvisionalPatent Application No. 60/578,236. Exemplary sizes of the nanocrystalsare also described herein.

In suitable embodiments, the luminescent nanocrystals comprise CdSe orZnS. Exemplary core/shell nanocrystals that can be utilized includeCdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS and CdTe/ZnS,nanocrystals. In exemplary embodiments, as described herein, thenanocrystals are dispersed or embedded in a polymeric matrix. Thismatrix can then be drawn into, or otherwise disposed in, a capillary,prior to sealing the capillary.

In additional embodiments, a scattering material (e.g., particles ofmaterial that scatter light entering the hermetically sealed containers)can be added to the matrix. Suitably, the scattering media are metallic,polymeric, semiconductor, or other material particles on the order of500 nm to microns to even millimeters in size. In other embodiments, ascattering material can be placed between the LED and the hermeticallysealed container, or between the container and the light guide.

The concentration of nanocrystals in the hermetically sealed containerwill depend on the application, size of the nanocrystals, composition ofthe nanocrystals, composition of the polymeric matrix, and otherfactors, and can be optimized using routine methods in the art.Suitably, the luminescent nanocrystals are present at a concentration ofabout 0.01% to about 50%, about 0.1% to about 50%, about 1% to about50%, about 1% to about 40%, about 1% to about 30%, about 1% to about20%, about 1% to about 10%, about 1% to about 5%, or about 1% to about3%, by weight. Suitably, about 40% to about 80%, more suitably about 50%to about 70%, or about 60%, of the light from the LEDs is absorbed bythe nanocrystals, with the remaining light suitably passing through thehermetically sealed container. Suitably about 10% to about 40%, or about20% to about 30% of the light that impacts the container passes throughthe container without being down-converted.

As described herein, hermetically sealed container 708 is opticallycoupled to both LED 702 as well as light guide 712. As used herein,“optically coupled” means that a component, (e.g., hermetically sealedcontainer and LED) are positioned so that light is able to pass from onecomponent to another component without substantial interference. Opticalcoupling includes embodiments in which hermetically sealed container 708and LED 702 are in direct physical contact, or as shown in FIG. 7A,suitably hermetically sealed container 708 (and thus nanocrystals 710)and LED 702 are spaced apart by a distance 704. While hermeticallysealed container 708 is shown in FIG. 7A contacting the top of substrate706, any suitable configuration can be utilized, so long as light fromLED is able to pass to hermetically sealed container 708. For example,hermetically sealed container can be positioned within the space betweenthe top of substrate 706 and LED 702. In other embodiments, an opticallytransparent element (e.g., a glass or plastic sheet or strip, includinga lens) can be placed between hermetically sealed container 708 and LED704. It should be noted that optical coupling does not require physicalinteraction between the components. Rather, so long as light is able topass between the components they are considered optically coupled. Thespacing between hermetically sealed container 708 and LED 702 results inthe nanocrystals being remotely positioned from the LED. This remotelocation improves the characteristics (intensity, purity, colorrendering, etc.) of the light generated from the LED and thenanocrystals.

In embodiments, light guide 712 is optically coupled to the hermeticallysealed container 708 via glue, tape mechanical alignment alone, or thelike, and combinations thereof. As shown in FIG. 7A, suitably lightguide 712 is directly in contact with hermetically sealed container 708.Tape, glue or other fastening device can be utilized to maintain thephysical contact between the two elements. Suitably fastening device isoptically transparent, or substantially optically transparent, so asallow light to pass from the hermetically sealed container to the lightguide. This can also be accomplished, for example, by utilizing apolymeric light guide, that when heated, melts or deforms such thathermetically sealed container can be contacted to the light guide, andthen the light guide cooled, thereby facilitating the formation of aphysical adhesion or contact between the two elements.

FIGS. 8A-8C show additional configurations of the LED device describedin FIG. 7A. In FIG. 8A, light guide 712 is shown with a tapered edge802. Tapered edge 802 can help facilitate directing the light emittedfrom the LED and the nanocrystals into light guide 712. In FIG. 8B,hermetically sealed container 708 can be embedded into light guide 712,as shown at 804. This can be accomplished by, for example, removing asection of light guide 712 such that hermetically sealed container canbe directly inserted into light guide 712. In other embodiments, asnoted above, light guide 712 can be heated so as to melt or deform,thereby allowing hermetically sealed container 708 to be inserted orembedded into light guide 712. As illustrated in FIG. 8C, in furtherembodiments, hermetically sealed container 708 can be shaped, as shownin 806. In exemplary embodiments, hermetically sealed container 708 canbe shaped so as to act as a lens or other optical device to improvelight transfer from the LED to the light guide.

FIG. 9 shows an embodiment of an LED device of the present invention inwhich the device further comprises one or more reflectors 902 positionedwith respect to the LED, light guide and hermetically sealed container,so as to increase the amount of light that is emitted from the lightguide. As shown in FIG. 9, in exemplary embodiments a reflector can bepositioned behind the LED so as to reflect any light emitted from thenanocrystals in the hermetically sealed container that is not directedinto the light guide, or light that bounces back from LED. Similarly,the sides of the hermetically sealed container can also comprisereflectors 902 so as to reflect light toward the light guide. Inadditional embodiments, the substrate on which the LED is positioned canalso comprise reflective, angled sides that help to direct light fromthe LED into the hermetically sealed container.

FIGS. 10A-10B provide illustrations of an exemplary hermetically sealedcontainer 708, e.g., a capillary. As shown in FIG. 10B, in embodiments,the end of hermetically sealed container 708 (capillary) can be cappedwith a cap 1002. Cap 1002 is suitably made from a polymeric materialthat can be heated prior to application, and then cooled so as to sealthe hermetically sealed container. In other embodiments, a liquidpolymeric solution can be used to fill the end of the hermeticallysealed container, thereby sealing the container. Additional methods ofsealing the hermetically sealed container, as described herein orotherwise known in the art, for example crimping, pinching, lasersealing, heat shrinking or otherwise closing the end of the container,can also be used.

Suitably, a solution of luminescent nanocrystals dispersed in apolymeric matrix is drawn into a capillary, for example by using avacuum to generate a reduced pressure. The polymer is then suitablycooled and cured. The curing process can often result in small bubblesforming in the polymeric matrix. It has been discovered that the smallsize of the bubbles in these preparations does not interfere with theoptical properties of the composition or the nanocrystals, and in fact,the presence of these small bubbles may aid in reducing pressure thatbuilds when the matrix is thermally cycled during manufacturing or usewith an LED.

In suitable embodiments, the present invention provides white lightlight-emitting diode (LED) devices. Such devices suitably comprise ablue light light-emitting LED and a hermetically sealed containercomprising a plurality of luminescent nanocrystals (suitably CdSe/ZnSluminescent nanocrystals) optically coupled to the LED. The device alsocomprises a light guide optically coupled the hermetically sealedcontainer.

As illustrated in FIG. 7B, as a first portion of blue light 718 emittedfrom the LED enters the hermetically sealed container, the light isdown-converted by the luminescent nanocrystals (e.g., CdSe/ZnSluminescent nanocrystals) to green light and red light (722 and 724). Asecond portion of blue light emitted from the LED 720, the green lightand the red light, are emitted from the light guide and combine toproduce white light 726.

As described herein, the white light LED devices of the presentinvention suitably comprise a hermetically sealed container comprisingluminescent nanocrystals spaced apart (remote) from the LED. Theconcentration of nanocrystals within the hermetically sealed containeris provided such that a portion of the blue light emitted by the LED isable to pass through the container without being absorbed by thenanocrystals. Another portion of the blue light is absorbed, and thendown-converted by the nanocrystals and emitted as green and red light.The red, blue and green light then combine to produce white light whenemitted from the light guide. The approach of the present inventiondiffers from white light LEDs in which three separate light sources(e.g., three LEDs) are utilized, or where all of the blue light from theLED is absorbed by the luminescent nanocrystals. By optimizing theconcentration/density and characteristics of the nanocrystals, highintensity, high purity, precisely color tuned, white light can beproduced.

In further embodiments, the present invention provides light-emittingdiode (LED) devices, comprising an LED, a hermetically sealed containercomprising a plurality of luminescent nanocrystals optically coupled tothe LED, and a light guide optically coupled to the hermetically sealedcontainer. Light emitted from the LED is down-converted by thenanocrystals, and exits a surface of the light guide. Suitably, theluminescent nanocrystals emit blue, green and red light, and the lightcombines to produce white light. In such embodiments, the LED suitablyemits ultraviolet light.

In further embodiments, the present invention provides display systemscomprising the LED devices described herein. Suitably, as shown in FIG.11, the display systems 1100 comprise a display 1102, and a plurality ofLED devices 700. As described herein, suitably LED devices 700 comprisean LED 702 and a hermetically sealed container 708 comprising aplurality of luminescent nanocrystals optically coupled to the LED. Thedevices also comprise a light guide 712 optically coupled to thehermetically sealed container. As shown in FIG. 11, suitably, display1102 at least partially encloses light guide 712.

In embodiments, down converted light emitted from the luminescentnanocrystals is emitted from the light guide and displayed on thedisplay. The display systems of the present invention are capable ofemitting light over the full range of the visible spectrum, includingwhite light.

In further embodiments, a first portion of light emitted from the LED isdown-converted by the luminescent nanocrystals. A second portion oflight emitted from the LED and the down-converted light from theluminescent nanocrystals are emitted from the light guide and displayedon the display. The display systems of the present invention are capableof emitting light over the full range of the visible spectrum, includingwhite light. In exemplary embodiments, the LEDs utilized emit bluelight.

Exemplary hermetically sealed containers (including capillaries) andluminescent nanocrystals are described herein. As shown in FIG. 11,suitably a single hermetically sealed container 708′ is opticallycoupled to at least two LEDs. A single hermetically sealed container canbe optically coupled to two or more, three or more, four or more, fiveor more, ten or more, etc., LEDs. While a hermetically sealed container708 can be coupled to each individual LED, in the display systemembodiments of the present invention, use of a single hermeticallysealed container which is coupled to multiple LEDs allows for easierassembly and manufacture of the display systems. In embodiments in whicha single hermetically sealed container is coupled to multiple LEDs, eachLED suitably emits blue light, a portion of which is down-converted bythe nanocrystals in the container, and a portion of which is emittedfrom the light guide. While FIG. 11 demonstrates an embodiment in whicha single light guide and a single display are utilized, it should beunderstood that the display systems of the present invention cancomprise multiple light guides and multiple displays optically coupledto each other to result in a display system.

The hermetically sealed containers comprising luminescent nanocrystalsas described herein can be utilized to retrofit existing LED displaysystems. By including the hermetically sealed containers (e.g.,capillaries) between the LEDs and light guides of a display, a portionlight from the LEDs (suitably blue light) can be converted to anydesired color, including combining with the LED light to produce whitelight.

Table 1 below shows the light output from luminescent nanocrystals ofthe present invention, as well as light from the blue LED used to excitethe nanocrystals. The nanocrystals were spaced apart from the LED(remote from the LED) as described herein. Data is also shown fortraditional Yttrium Aluminum Garnet (YAG) phosphors. FWHM=full width athalf maximum.

TABLE 1 Spectrum Characteristics YAG Luminescent Nanocrystals Blue Peak(nm) 451.8 463.5 Blue FWHM (nm) 21.6 21.6 Green Peak (nm) N/A 535.3Green FWHM (nm) N/A 32.8 Yellow Peak (nm) 559 N/A Yellow FWHM (nm) 105N/A Red Peak (nm) N/A 614.5 Red FWHM (nm) N/A 44.5

Luminescent Nanocrystal Composites

In a still further embodiment, the present invention luminescentnanocrystal composite materials 1200. As shown in FIG. 12, inembodiments, the composite materials comprise a first polymeric material1204 having a first composition, a second polymeric 1202 material havinga second composition, and a plurality of luminescent nanocrystals 710dispersed in second polymeric material 1202. The, second polymericmaterial 1202 is dispersed in first polymeric material 1204.

Dispersing luminescent nanocrystals in second polymeric material 1202provides a method to seal the nanocrystals and provide a mechanism formixing various compositions and sizes of nanocrystals. Suitable secondpolymeric materials 1202 include aminosilicone, as well as otherpolymers described herein, including, but not limited to, poly(vinylbutyral):poly(vinyl acetate); epoxies; urethanes; silicone andderivatives of silicone, including, but not limited to,polyphenylmethylsiloxane, polyphenylalkylsiloxane, polydiphenylsiloxane,polydialkylsiloxane, fluorinated silicones and vinyl and hydridesubstituted silicones; acrylic polymers and copolymers formed frommonomers including but not limited to, methylmethacrylate,butylmethacrylate and laurylmethacrylate; styrene based polymers; andpolymers that are cross linked with difunctional monomers, such asdivinylbenzene.

While second polymeric material 1202 provides a suitable environment fordispersing the nanocrystals, the polymers that provide efficient mixingof the nanocrystals can often be brittle or difficult to shape or mold.Dispersing the nanocrystal/polymer mixture 1202 in a further polymericmaterial 1204 allows for the production of a composite that maintainsthe desired optical/down-conversion characteristics of the luminescentnanocrystals, while also maintaining a hermetically sealed compositionthat is also able to be mechanically worked as desired. Exemplarypolymeric materials for use as first polymeric material 1204 includeepoxies and polycarbonates. Exemplary epoxies and polycarbonates arewell known in the art.

Suitably the luminescent nanocrystals dispersed in the compositematerials absorb light (e.g., blue light) and emit green light and/orred light, though other colors can also be emitted from thenanocrystals. Exemplary nanocrystals for use in the composite materialsare described herein and include nanocrystals comprise that CdSe or ZnS,as well as core/shell luminescent nano crystals comprising CdSe/ZnS,InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS.

In further embodiments, the composites can comprise an inorganic layer1206 that hermetically seals the composite. Examples of inorganic layersare described herein, and include, SiO₂, TiO₂ or AlO₂.

Suitably, the composite materials of the present invention have anoptical density of about 0.5 to about 0.9 at the blue LED wavelength anda path length of about 50 μm to about 200 μm. Suitably, the compositeshave an optical density of about 0.5 to about 0.8, about 0.7 to about0.8, or about 0.8 at the blue LED wavelength. Suitably, the path lengthof the composite materials is about 75 μm to about 150 μm, or about 100μm. The concentration of luminescent nanocrystals utilized in thecomposite materials of the present invention is suitably about the sameas the concentration utilized in the hermetically sealed compositionsdescribed herein. Thus, the luminescent nanocrystals are suitablypresent at a concentration of about 0.01% to about 50%, about 0.1% toabout 50%, about 1% to about 50%, about 1% to about 40%, about 1% toabout 30%, about 1% to about 20%, about 1% to about 10%, about 1% toabout 5%, or about 1% to about 3%, by weight, such that about 40% toabout 80%, more suitably about 50% to about 70%, or about 60%, of thelight that impacts the composite is absorbed by the nanocrystals.

The present invention also provides methods of preparing luminescentnanocrystal composite materials. As shown in flowchart 1300 of FIG. 13,with reference to FIG. 12, suitably such methods include step 1302,comprising dispersing a plurality of luminescent nanocrystals 710 in afirst polymeric material 1202 to form a mixture of the luminescentnanocrystals and the first polymeric material. The mixture is then curedin 1304. In 1308, a particulate is generated from the cured mixture. Instep 1310, the particulate is dispersed in a second polymeric material1204 to generate a composite material. The particulate can be dispersedin the second polymeric material using various forms of mechanicalmixing when the second polymeric material is in a liquid, or mostlyliquid, state.

Exemplary polymeric materials for use in the methods are describedherein, as are suitable luminescent nanocrystals. Suitably, theluminescent nanocrystals comprise CdSe or ZnS, or are core shellnanoparticles comprising CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdSor CdTe/ZnS, and are suitably dispersed in aminosilicone.

Suitably the mixture of luminescent nanocrystals and the first polymericmaterial are mechanically processed to form the particulate. Examples ofmechanical processing include ball milling, grinding, pulverizing,crushing or otherwise forming a particulate from the mixture. Chemicalor other treatments can also be utilized to generate a particulate.Suitably the particulate is a powder. Suitably, the particulate of themixture of the nanocrystals and the first polymeric material has a sizeon the order of about 10 μm to about 200 μm, or about 10 μm to about 100μm, or about 20 μm to about 70 μm, or about 50 μm.

Other structures of the mixture of the luminescent nanocrystals and thefirst polymeric material beyond particulates can also be generated, forexample, films, rods, ribbons, spheres, etc. These structures can thenbe dispersed in the second polymeric material.

In further embodiments, the second polymeric material can be replacedwith other materials, such as ceramics, glasses, or inorganic materialsthat have the desired optical and physical properties of the finaldesired product.

In exemplary embodiments, a cross-linker is added in step 1306 to themixture prior to the curing in 1304. Exemplary cross-linkers aredescribed herein or otherwise known in the art.

In further embodiments, as shown in FIG. 13, the methods can furthercomprise step 1312 of forming the composite material into a film.Suitably, the composite mixture is cast onto a substrate, such as anon-stick substrate, for example a sheet of TEFLON®. After the mixturehas been cured, the cured film can be removed from the non-sticksubstrate. The film can then be cut or diced into any desired size orshape.

In additional embodiments, as shown in step 1314 of flowchart 1300, aninorganic layer can be disposed on the composite so as to provide afurther hermetic seal to the composite. The inorganic layer can bedisposed after formation of the composite material, but prior toformation of the composite into a film, or the inorganic layer can bedisposed following the film formation (including followingdicing/cutting into a desired shape). Methods of disposing an inorganiclayer on the composite are described herein, and include various methodsof coating, spraying, ALD, dipping etc.

The composite material can also be extruded, molded, solvent cast,compression molded, etc., to form the desired shape and configuration ofthe composite. Methods and parameters for carrying out these techniquesare well known in the art.

The composite materials of the present invention can be utilized in thedown-converting applications as described herein, or in otherapplications where a down-converting layer/film/structure is desired.Thus, in exemplary embodiments, a layer, film, tube, strip or othersuitable structure can be prepared from the composite materials andoptically coupled to an LED (and/or a light guide) so as to provide thedown-conversion of light from an LED as described herein.

Light Guides Comprising Nanocrystals

In a still further embodiment, the present invention provideslight-emitting diode (LED) devices as shown in FIGS. 14A-14B. Suitably,LED devices 1400 and 1401 comprise an LED 702, and a light guide 712optically coupled to the LED. A plurality of luminescent nanocrystals710 are dispersed in a region (1404, 1404′) within the light guide.Suitably, the region extends along a length 1410 of the light guide.Suitably, the nanocrystals emit blue light, red light and green light.In embodiments, the LED is an ultraviolet (UV) light emitting LED.

In further embodiments, a first portion of light emitted from the LED isdown-converted by the nanocrystals. As shown in FIGS. 14A and 14B asecond portion of light (1412) emitted from the LED, and thedown-converted light (1414 and 1416), exit a surface of the light guide.

As described throughout, luminescent nanocrystals of the presentinvention suitably absorb light of a specified wavelength and thendown-convert the absorbed light, emitting light at a differentwavelength. In the embodiments of the present invention illustrated inFIGS. 14A-14B, the luminescent nanocrystals 710 are dispersed in aregion 1404 and 1404′ of the light guide. Light that is emitted from theLED travels through the length of the light guide 1410, suitablyreflecting off of reflectors along the surface of the light guide. Inembodiments, a portion of the light emitted from the LED is emitted fromthe surface of the light guide as shown at 1412. A further portion ofthe light emitted from the light guide is absorbed by the luminescentnanocrystals and down-converted. This down converted light (1414 and1416) is then emitted from the light guide. In further embodiments, allof the light emitted from the LED is down-converted by the nanocrystals.

In exemplary embodiments, the LED is a blue light emitting LED. Asdiscussed in detail herein, in exemplary embodiments, a portion of theblue light emitted from the LED is down-converted by the luminescentnanocrystals into red light and green light. When the emitted green 1414and red 1416 light combine with the portion of blue light 1412 emittedfrom the LED (that has not been down-converted), white light is emittedfrom the surface of the light guide. In suitable embodiments, lightguide 712 comprises one or more features 1406 on the emitting surface(s)of the light guide. Features 1406 are suitably patterns etched into, orformed from, the surface of light guide 712 that aid in the transmissionof light from the light guide. In embodiments, features 1406 aredesigned to enhance the emission of light that is emitted directly fromthe LED (including blue light).

In further embodiments, the LED is a UV light emitting LED, andsubstantially all of the light emitted from the LED is down-converted bythe nanocrystals to red, green and blue light. The light is then emittedfrom the light guide and combines to produce white light.

Exemplary nanocrystals for use in the regions within the light guidesare described herein. Suitably, the nanocrystals CdSe or ZnS, or arecore/shell nanocrystals, suitably comprising CdSe/ZnS, InP/ZnS,PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS.

As used herein, “region” refers to a section or portion of the lightguide into which luminescent nanocrystals have been disposed. Suitably,as shown in FIGS. 14A-14B, regions 1404 and 1404′ extend along thelength 1410 of light guide 712. The length 1410 of the light guide isthe lateral dimension extending perpendicular (or substantiallyperpendicular) to the LED. By orienting light guide 712 with respect toLED 702 as shown in FIGS. 14A and 14B, light from LED 702 impacts agreater portion of the nanocrystals 710 within the regions 1404 and1404′ prior to exiting the light guide. Suitably, region 1404/1404′ is alayer of luminescent nanocrystals. The dimensions of region 1404/1404′are dictated by the overall dimensions of the light guide, thoughgenerally the thickness of the region will be in proportion to the sizeof the LED (i.e., on the order of 10s of microns to 10s of millimetersor so), while the dimensions in the plane of the light guide (i.e.,length and width), suitably span the entire light guide. In otherembodiments, the region comprising the nanocrystals can be throughoutthe entire light guide in all dimensions (i.e., dispersed throughout thelight guide).

Region 1404/1404′ can be generated by dispersing nanocrystals in apolymeric matrix and then forming the light guide around the polymereither prior to or after curing the polymer. Alternatively, the lightguide can be prepared and then nanocrystals injected, painted, sprayed,or otherwise deposited so as to form the region. Other methods forgenerating a polymeric matrix, including the methods described hereinwith regard to formation of polymeric composites can also be utilized toform the regions. In exemplary embodiments, the luminescent nanocrystalcomposite materials 1200 described herein can be utilized to prepare theregions in the light guides.

Dispersing luminescent nanocrystals in a region within the light guideprovides numerous benefits and advantages to the overall system. Forexample, more uniform illumination of the nanocrystals can be achieved,thereby reducing the presence of local hot spots. Dispersing thenanocrystals throughout the region allows for improved heat dissipationfrom the nanocrystals, thus lowering the overall temperature of thenanocrystals. By reducing the optical path length from the nanocrystalsto the top surface of the light guide, any loss in efficiency due toreabsorption of green and red photons is reduced. In addition, a lowconcentration of nanocrystals can be utilized in the region, thuslowering possible photo- and thermal-induced interactions betweennanocrystals and the material in which the nanocrystals are dispersed(e.g., a polymer), thereby increasing system life-time.

The concentration of luminescent nanocrystals in the region of the lightguide will depend on the application, size of the nanocrystals,composition of the nanocrystals, composition of the polymeric matrix,and other factors, and can be optimized using routine methods in theart. Suitably, the luminescent nanocrystals are present at aconcentration that is less than the concentration utilized in the LEDdevice embodiments described herein utilizing a hermetically sealedcontainer, suitably about 0.01% to about 50%, about 0.1% to about 50%,about 1% to about 50%, more suitably about 1% to about 40%, about 1% toabout 30%, about 1% to about 20%, about 1% to about 10%, about 1% toabout 5%, or about 1% to about 3%, by weight. In general, theconcentration of luminescent nanocrystals scales proportionally based onthe size of the light guide. Thus, the concentration of luminescentnanocrystals utilized in a hermetically sealed container having athickness of approximately 100 mm will be reduced by two orders ofmagnitude for a light guide that is about 10 cm in length, for example.

In exemplary embodiments, region 1404′ has a thickness that varies alongthe length 1410 of the light guide. As shown in FIG. 14B, suitably thethickness of region 1404′ increases along the length 1410 of the lightguide, from a minimum 1406 at the LED, to a maximum at the far end ofthe light guide 1408, away from the LED. In exemplary embodiments, thethickness increases approximately linearly along the length of the lightguide. In further embodiments, the thickness can increase in anon-linear manner, and/or can achieve a maximum thickness beforereaching the far end of the light guide 1408. It should be noted thatthe schematic shown in FIG. 14B showing the thickness of region 1404′increasing linearly both along the top and bottom of the region is forillustrative purposes only and any appropriate shape/orientation ofregion 1404′ can be utilized. Varying the thickness of the regionprovides more uniform light illumination from the light guide.

FIGS. 15A-15C show the intensity of light emitted from the light guideshown in FIG. 14A. The intensity is shown as a function of relativedistance along the light guide, beginning at zero (0), adjacent the LED(1406), to one (1), the far end of the light guide away form the LED(1408). FIG. 15A shows the intensity of blue light that is both emittedfrom the LED (going forward) and reflected within the light guide priorto being emitted. FIG. 15B shows the intensity of green and red lightemitted from the nanocrystals resulting from both blue light that isabsorbed directly from the LED (going forward) as well as blue lightthat is reflected. Finally, FIG. 15C illustrates a plot of intensityshowing the combined sum of all blue light emitted from the light guide(sum of blue), as well as the combined sum of all green and red light(sum of green/red). As demonstrated in FIG. 15C, the intensity of boththe blue light and the green/red light diminishes along the length ofthe light guide. The blue light diminishes as a result of absorbancethroughout the length of the light guide. As the amount of nanocrystalsin the region of the light guide are constant (due to a uniformthickness of the region), the intensity of the red and green light alsoreduce along the length of the light guide.

FIGS. 16A-16C show intensity plots similar to those in FIGS. 15A-15C,but for the light guide configuration illustrated in FIG. 14B (region1404′ with nanocrystals that has a varying thickness). The amount ofblue light emitted both going forward and reflected are similar to theconstant thickness region. However, in comparing the intensity ofgreen/red light in FIGS. 16B-16C to 15B-15C, it can be seen that abetter uniformity of green/red light is emitted from the light guidehaving the region with varying thickness (1404′). This is most likely aresult of the increased thickness of region 1404′ at the end of thelight guide away from the LED. As there are more nanocrystals present atthe far end of the light guide (even though the concentration may beconsistent throughout the light guide), more blue light can be absorbedand down-converted into green and red light.

The present invention also provides display systems comprising adisplay, a plurality of LEDs and a light guide optically coupled theLEDs, wherein the display at least partially encloses the light guide.As described herein, a plurality of luminescent nanocrystals aredispersed in a region within the light guide, the region extending alonga length of the light guide. Light from the LED is down-converted by thenanocrystals, exits the light guide, and is displayed on the display. Inembodiments, the LED is a UV light emitting LED and the nanocrystalsemit red, green and blue light.

In other embodiments, a first portion of light emitted from the LED isdown-converted by the luminescent nanocrystals, and a second portion oflight emitted from the LED and the down-converted light from theluminescent nanocrystals are emitted from the light guide and displayedon the display. As described herein, in exemplary embodiments the LEDemits blue light, and the first portion of blue light emitted from theLED is down-converted by the luminescent nanocrystals to green light andred light. Suitably, the second portion of blue light, the green lightand the red light combine to produce white light.

Exemplary nanocrystals, including core shell nanocrystals, are describedherein. In exemplary embodiments the light guide comprises one or morereflectors.

Suitably, the region comprising the luminescent nanocrystals is a layerof nanocrystals. In exemplary embodiments, the thickness of the regionvaries along the length of the light guide, suitably increasing from theLED along the length of the light guide, for example, linearly, asdescribed herein.

EXAMPLES

The following examples are illustrative, but not limiting, of the methodand compositions of the present invention. Other suitable modificationsand adaptations of the variety of conditions and parameters normallyencountered in nanocrystal synthesis, and which would become apparent tothose skilled in the art, and are within the spirit and scope of theinvention.

Example 1 Preparation of Hermetically Sealed Containers

A rectangular tube of approximate dimensions 3 mm×0.5 mm with a 2 mm×0.5mm cavity is prepared by extrusion of PMMA. The length of tubing is thenfilled with a solution comprising fluorescent luminescent nanocrystals.The luminescent nanocrystal solution is then cured. Segments of thetubing are then heat sealed to trap the nanocrystals in the tubing.Suitably the filling and sealing are performed in an inert atmosphere. Abarrier layer (e.g., SiO₂, TiO₂ or AlO₂) can then be disposed on theouter surface of the tubing.

A drawn glass capillary can also be used to prepare a hermeticallysealed container comprising nanocrystals. The end of the capillary issealed either via melt sealing or plugging with a solder or adhesive orsimilar structure. The capillary can be filled with a solution ofluminescent nanocrystals such that the entire volume of the capillary isfilled with the same nanocrystal solution, or the capillary can befilled in stages, such that different nanocrystals are separated alongthe length of the capillary. For example, a first luminescentnanocrystal solution can be introduced into the capillary, and then aseal placed adjacent to the solution (for example, but melt sealing orplugging the capillary). A second luminescent nanocrystal solution canthen be added to the capillary, and again, a seal placed adjacent to thesolution. This process can be repeated as often as required until thedesired number of individual, hermetically sealed nanocrystal segmentsare created. In this manner, different compositions of luminescentnanocrystals can be separated from each other in the same container,thereby allowing the production of containers comprising multiplecompositions (e.g., colors) of luminescent nanocrystals. In a similarembodiment, a multi-lumen capillary can be used in which differentcompositions of luminescent nanocrystals (e.g., those which emitdifferent colors) can be introduced and thus kept separate from eachother, and still be hermetically sealed from external air and moisture.

Example 2 Preparation of Nanocrystals Composite Materials

Luminescent nanocrystals (e.g., CdSe/ZnS) that emit red (630 nm) andgreen (530 nm) light are mixed at a 3% weight concentration into anaminosilicone polymer. The aminosilicon polymer has a viscosity of 350centipoises, and comprises 5% amino groups and 95% dimethylsiloxane. Theresulting composition has an optical density of about 0.8 and a pathlength of 100 μm.

An epoxide cross linker is added and the material is cured to form arubber. The cured quantum dot composition is then placed into a ballmill and ground into a 50 μm powder.

The powder is then mixed into a two part epoxy at about 30% loading, andthe polymer is degassed. The refractive index of the nanocrystals andthe epoxy are suitably matched so as to minimize light scattering andthe resulting absorptions by the nanocrystals.

The epoxy/nanocrystal mixture is cast onto a TEFLON® sheet at athickness of about 300 μm. After curing, the film is removed. Theoptical density of the final composite material is about 0.8 OD.

Exemplary embodiments of the present invention have been presented. Theinvention is not limited to these examples. These examples are presentedherein for purposes of illustration, and not limitation. Alternatives(including equivalents, extensions, variations, deviations, etc., ofthose described herein) will be apparent to persons skilled in therelevant art(s) based on the teachings contained herein. Suchalternatives fall within the scope and spirit of the invention.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent or patent application wasspecifically and individually indicated to be incorporated by reference.

What is claimed is:
 1. A display system comprising: a. a display; b. aplurality of light emitting diodes (LEDs); c. a light guide opticallycoupled to the LEDs; and d. a composition comprising a plurality ofphosphors placed between the display and the light guide.
 2. The displaysystem of claim 1, wherein the phosphors are luminescent nanocrystals.3. The display system of claim 2, wherein the luminescent nanocrystalscomprise CdSe or ZnS
 4. The display system of claim 2, wherein theluminescent nanocrystals are core/shell luminescent nanocrystalscomprising CdSe/ZnS, InP/ZnS, PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS.5. The display system of claim 1, wherein the phosphors are YAGphosphors.
 6. The display system of claim 1, wherein the LEDs are blueLEDs.
 7. The display system of claim 1, wherein the light guide furthercomprises one or more features that aid in the transmission of lightfrom the light guide.
 8. The display system of claim 1, wherein thecomposition is a film.
 9. The display system of claim 8, wherein thefilm comprises a polymeric matrix in which the phosphors are dispersed.10. The display system of claim 9, wherein the polymeric matrixcomprising a first polymeric material that is an epoxy or apolycarbonate and a second polymeric material that is an aminosilicone.11. The display system of claim 1, wherein the light guide is opticallycoupled to the LEDs with glue.
 12. The display system of claim 1,wherein the light guide is optically coupled to the LEDs with tape. 13.The display system of claim 1, wherein the light guide is opticallycoupled to the LEDs with mechanical alignment.
 14. The display system ofclaim 1, wherein the light guide is physically coupled to the LEDs. 15.A display system comprising: a. a display; b. a plurality of blue lightemitting diodes (LEDs); c. a light guide optically coupled to the LEDs;and d. a composition comprising a plurality of luminescent nanocrystalsplaced between the display and the light guide.
 16. The display systemof claim 15, wherein the luminescent nanocrystals comprise CdSe or ZnS17. The display system of claim 15, wherein the luminescent nanocrystalsare core/shell luminescent nanocrystals comprising CdSe/ZnS, InP/ZnS,PbSe/PbS, CdSe/CdS, CdTe/CdS or CdTe/ZnS.
 18. The display system ofclaim 15, wherein the light guide further comprises one or more featuresthat aid in the transmission of light from the light guide.
 19. Thedisplay system of claim 15, wherein the composition is a film.
 20. Thedisplay system of claim 19, wherein the film comprises a polymericmatrix in which the luminescent nanocrystals are dispersed.
 21. Thedisplay system of claim 20, wherein the polymeric matrix comprising afirst polymeric material that is an epoxy or a polycarbonate and asecond polymeric material that is an aminosilicone.
 22. The displaysystem of claim 15, wherein the light guide is optically coupled to theLEDs by mechanical alignment.
 23. The display system of claim 15,wherein the light guide is optically coupled to the LEDs with tape. 24.The display system of claim 15, wherein the light guide is opticallycoupled to the LEDs with mechanical alignment.
 25. The display system ofclaim 15, wherein the light guide is optically coupled to the LEDs withglue.